The Food and Drug Administration is warning physicians that women who suffer migraine headaches and are pregnant or may become pregnant should not use the drugs valproate or valproic acid to prevent the severe headaches, in light of new evidence showing those taking the drugs during pregnancy have children with lower IQ scores than women who do not take them.

That warning represents a strengthening of a boxed warning that already appears on these prescription medications, which are used to control epileptic seizures, to treat bipolar disorder, and to prevent and relieve migraine headaches. Also known by the commercial names Depakote, Depacon and Depakene, valproate medications have been linked to birth defects in babies when taken by their mothers in pregnancy.

A recent study also linked the drugs, taken in pregnancy, to a higher risk of autism in children.

"Valproate medications should never be used in pregnant women for the prevention of migraine headaches because we have even more data now that show the risk for the children outweighs any treatment benefits for this use," said Dr. Russell Katz of the FDA Center for Drug Evaluation and Research.

Katz said there may be "some value" in using the medications in treatment of a pregnant woman's epilepsy or bipolar disorder (sometimes known as manic depression) if other medications for those conditions have not proven effective.

The warning comes after the publication of a trial called "Neurodevelopmental Effects of Anti-Epileptic Drugs," which found that compared with children born of mothers who took other anti-seizure drugs, 6-year-olds whose mothers took valproic acid or valproate had IQ scores that were on average eight to 10 points lower.